Silvia Bautista-Baños

Effects of chitosan and plant extracts on growth of Colletotrichum gloeosporioides, anthracnose levels and quality of papaya fruit

The objectives of this research were to evaluate the in vitro fungicidal effect of chitosan and aqueous extracts of custard apple leaves, papaya leaves and papaya seeds, and the combination of chitosan and plant extracts on the development of Colletotrichum gloeosporioides, which causes anthracnose on papaya. Chitosan at 2.0% and 3.0% had a fungicidal effect on C. gloeosporioides. Extracts alone did not show any fungicidal effect while the combination of 2.5% chitosan with all the tested extracts had a fungistatic rather than fungicidal effect. Changes in the conidial morphology of C. gloeosporioides were observed with 1.5% chitosan concentration after 7 h incubation. For in situ studies, control of anthracnose disease was obtained with 1.5% chitosan applied before C. gloeosporioides inoculation. Phomopsis was most frequently isolated from the non-inoculated fruit. Chitosan applications did not influence the content of total solid solubles or percentage weight loss during the storage of papaya fruit. However, there was a tendency toward greater firmness in fruit treated with the papaya seed extract alone or combined with chitosan.

Antifungal effects of chitosan with different molecular weights on in vitro development of Rhizopus stolonifer (Ehrenb.:Fr.) Vuill

Determination of the molecular weight of three types of chitosan was carried out by HPSEC-RI. The effect of low, medium and high molecular weight chitosan was evaluated on development of three isolates of Rhizopus stolonifer. Image analysis and electronic microscopy observations were done in spores of this fungus. Germination of R. stolonifer in potato dextrose broth with chitosan was also evaluated. Results pointed out that the low molecular weight chitosan was more effective for inhibition of mycelial growth while the high molecular weight chitosan affected spore shape, sporulation and germination. Studies of scanning and transmission electron microscopy revealed numerous and deeper ridge ornamentations of the chitosan-treated spore.

Seasonal evaluation of the postharvest fungicidal activity of powders and extracts of huamuchil (Pithecellobium dulce): action against Botrytris cinerea, Penicillium digitatum and Rhizopus stolonifer of strawberry fruit

The fungistatic or fungicidal effect of powders, and aqueous and ethanolic extracts of seeds, and monthly harvested leaves of huamuchil (Pithecellobium dulce ) were evaluated for fungicidal activity, against Botrytis cinerea , Penicillium digitatum , and Rhizopus stolonifer . Fungicidal activity of huamuchil powders and aqueous extracts were also evaluated on strawberry fruit during storage. Preliminary characterization of the active compound responsible for the fungicidal effect was carried out using thin layer chromatography and spectrophotometry. Results indicated that powders had the best fungicidal effect, in both in vitro and in situ studies. Fungistatic or fungicidal properties were associated with the plant organ and harvest month. A correlation between high absorbance values of extracts with the fungicidal or fungistatic effect was not observed. The highest fungistatic or fungicidal effect for both in vitro and in situ studies was recorded from extracts of leaves harvested in months having more stressful environmental conditions; the cold season (October/February) and, the dry, hot season (April and June). Attempts to characterize the active compound suggest that kaempferol may be responsible for the fungicidal effect. # 2003 Elsevier Science B.V. All rights reserved.

Release study and inhibitory activity of thyme essential oil-loaded chitosan nanoparticles and nanocapsules against foodborne bacteria

The antibacterial property of thyme essential oil due to different volatile compounds, has been well documented in the literature. To overcome the high volatility of essential oil components, encapsulation has emerged as a new alternative. In this work, chitosan and thyme essential oil-loaded chitosan nanoparticles (TEO-CSNPs) and nanocapsules (TEO-CSNCs) were prepared by nanoprecipitation and nanoencapsulation, respectively. The morphology, encapsulation efficiency, release kinetics, and inhibitory activity were evaluated. Average size of nanocapsules (9.1±1.6nm) was slightly higher than nanoparticles (6.4±0.5nm). The percentage encapsulation of thymol and carvacrol, more than 68%, was similar for nanoparticles and nanocapsules. However, thymol and carvacrol release time from TEO-CSNPs was faster compared to TEO-CSNCs. The release kinetics data were fitted to three analytical kinetic models with no statistical differences among them. The inhibitory activity was higher for nanoparticles than for nanocapsules when tested against six foodborne bacteria. The inhibitory effect of TEO-CSNPs was the highest against Staphylococcus aureus (inhibition halo 4.3cm) and for TEO-CSNCs it was against Bacillus cereus (inhibition halo 1.9cm).

Microscopic study of the morphology and metabolic activity of Fusarium oxysporum f. sp. gladioli treated with Jatropha curcas oil and derivatives

The fungus Fusarium oxysporum f. sp. gladioli is one of the main pathogenic microorganisms of the ornamental genus Gladiolus. The attack of this microorganism includes corms and different plant phenological stages. In this study, different microscopic techniques and fluorochromes were used to evaluate the effect of J. curcas oil and acylglycerides, namely trilinolein, triolein, monomyristin and dimyristin, on the morphology, membrane integrity (%), viability (%) and germination (%) of F. oxsporum f sp. gladioli. Phase-contrast optical photomicrographs and scanning microscopy showed that J. curcas oil and the triglycerides triolein and trilinolein caused the formation of numerous vacuoles, alterations in the morphology of the outer covering of the mycelium and conidia, and inhibition of membrane activity in the fungus during 24 h of incubation. The fluorochromes used detected no permanent damage to the viability of the conidia. The high germination percentage of the conidia of Fusarium oxysporum f. sp. gladioli indicates that the damage caused by the application of the treatments was fungistatic rather than fungicidal and did not cause cell death.

Biological Activity of Chitosan Nanoparticles Against Pathogenic Fungi and Bacteria

The application of nanotechnology has shown great potential in terms of developing new solutions for the agriculture and food sectors in controlling fungi and pathogenic bacteria. Concerning the biological activity of chitosan nanoparticles in foodborne bacteria, it has been demonstrated that their inhibitory effect depends mainly on particle size, concentration, and pH. Several studies have shown the effectiveness of incorporating other materials such as silver, copper, and metal ions with chitosan nanoparticles in the control of a variety of pathogenic bacteria. Other compounds, including food preservatives such as nisin and erythrosine, have also been reported to increase the bacterial activity of chitosan nanoparticles against Streptococcus mutans , Staphylococcus aureus , Pseudomonas aeruginosa , Candida albicans, and Listeria monocytogenes . In the control of phytopathogenic fungi, it has been reported that the development of the fungi Rhizopus sp., Colletotrichum capsici , Colletotrichum gloeosporioides, and Aspergillus niger was significantly inhibited with the application of chitosan nanoparticles. Currently, studies of the chitosan nanomaterials are mainly focused on aspects of in vitro control; therefore, it is necessary to perform in situ control assessments to provide solutions and alternatives to the problems of agricultural and food safety areas that are associated with pathogenic microorganisms. Further studies are also needed to explore the mechanism of action.

Cactus stem (Opuntia ficus-indica Mill): anatomy, physiology and chemical composition with emphasis on its biofunctional properties

Cactus stem (Opuntia ficus-indica Mill) is native to Mesoamerica and marketed in different forms such as fresh, frozen or pre-cooked. Worldwide, this vegetable is recognized for its pharmaceutical actions, including its antioxidant, diuretic, anticarcinogenic, anti-inflammatory, anti-diabetic, and anti-hypercholesterolemic properties, as well as their antiviral and antispermatogenic effects. However, not all of these properties have been associated with its chemical composition; therefore, this review aims to present and integrate information available on the physiology and anatomy of cactus stem and its chemical composition, focusing on some of the many factors that determine its biofunctionality.

Morphological and Ultrastructural Modifications of Chitosan-Treated Fungal Phytopathogens

Summary A number of studies have confirmed the in vitro fungicidal effect of chitosan on various phytopathogenic fungal families including among others, Mucoraceae, Pleosporaceae, and Glomerellaceae. Investigations of the morphology and ultrastructure of the chitosan-treated fungi in in vitro studies and during the plant-pathogen interaction of various pathosystems have been carried out by using conventional optical/light microscopy and with other advanced instruments including SEM, TEM, and confocal microscopy. The electrostatic interaction between chitosan and the microorganism is noted by dramatic alterations observed from the damaged structure of the cell wall and plasma membrane. The integrity of organelles including vacuoles was seriously affected, leading in some cases to lysis of the fungal cell. During the host-pathogen interaction, formation of structural barriers by the host, mainly through inter- and intracellular synthesis of phenolic-lignin-like material that stops fungal invasion, was also observed. Fungal growth was not beyond the outer cortical area of the infected tissues, while damage on fungi was similar to those observed in in vitro studies. Microscopic examinations have confirmed the fungicidal and eliciting properties of chitosan.

Evaluation of Physical Properties and Antibacterial Activity of Bioactive Compounds-Loaded Chitosan Nanoparticles

Bioactive compounds such as essential oils (EO), botanical extracts and natural resins are well known to have beneficial properties. Among these properties are their antibacterial activity. A disadvantage of these compounds is that they are volatile. Therefore, encapsulation is a good way to overcome this problem. In this study, the morphology, particle size distribution, Zeta potential and microbiological activity of chitosan nanoparticles incorporated with three different bioactive compounds having antimicrobial properties: ethanol extract of propolis, thyme essential oil and ethanol extract of Byrsonima crassifolia (L.) Kunth were evaluated. Nanoparticles were synthesized using the nanoprecipitation method. The morphology was observed using transmission electron microscopy (TEM). Also, particle size distribution and Zeta potential were measured. Results show spherical in shape nanoparticles. Thyme essential oil-loaded chitosan nanoparticles (TEO-CSNPs) showed the smallest particle size and highest stability as assessed by Zeta potential measurement, followed in stability by ethanol extract of propolis-loaded chitosan nanoparticles (EEP-CSNPs), ethanol extract of Byrsonima crassifolia (L.) Kunth (EEBC-CSNPs) and finally by chitosan nanoparticles (CSNPs). The antibacterial activity of the bioactive compounds-loaded chitosan nanoparticles was evaluated against Staphylococcus aureus. The highest antibacterial activity was observed for TEO-CSNPs with an inhibition halo (IH) value of 10.54±0.78 mm, followed by EEP-CSNPs (8.10±1.19 mm). EEBC-CSNPs and CSNPs did not show zone of inhibition. Bioactive compounds-loaded chitosan nanoparticles represents a good alternative for bacterial control of food borne pathogens in applications for fruits and vegetables conservation.

Use of inductors in the control of Colletotrichum gloeosporioides and Rhizopus stolonifer isolated from soursop fruits: in vitro tests

Soursop (Annona muricata) is a tropical fruit that can be infected by Colletotrichum gloeosporioides and Rhizopus stolonifer. Traditional methods used for postharvest disease control include the application of fungicides, however due to their excessive use, as well as their persistence in the environment, the development of new strategies that control pathogens are required. The application of chitosan (Chi), salicylic acid (SA) and methyl jasmonate (MJ) is an environmentally-friendly alternative with antimicrobial properties and also induces defense mechanisms in plant tissues. In this study, Colletotrichum was reactivated and Rhizopus was identified using morphological features and molecular tools. In vitro, the application of 0.5 and 1.0% of Chi alone or in combination with SA and MJ decreased mycelial growth and sporulation, a complete inhibition of spore germination was obtained. Thus, the application of Chi in combination with SA and MJ could be a smart strategy to inhibit the development of pathogens that attack soursop fruit.